1,307 research outputs found
Collisional decay of 87Rb Feshbach molecules at 1005.8 G
We present measurements of the loss-rate coefficients K_am and K_mm caused by
inelastic atom-molecule and molecule-molecule collisions. A thermal cloud of
atomic 87Rb is prepared in an optical dipole trap. A magnetic field is ramped
across the Feshbach resonance at 1007.4 G. This associates atom pairs to
molecules. A measurement of the molecule loss at 1005.8 G yields K_am=2 10^-10
cm^3/s. Additionally, the atoms can be removed with blast light. In this case,
the measured molecule loss yields K_mm=3 10^-10 cm^3/s
Network growth models and genetic regulatory networks
We study a class of growth algorithms for directed graphs that are candidate
models for the evolution of genetic regulatory networks. The algorithms involve
partial duplication of nodes and their links, together with innovation of new
links, allowing for the possibility that input and output links from a newly
created node may have different probabilities of survival. We find some
counterintuitive trends as parameters are varied, including the broadening of
indegree distribution when the probability for retaining input links is
decreased. We also find that both the scaling of transcription factors with
genome size and the measured degree distributions for genes in yeast can be
reproduced by the growth algorithm if and only if a special seed is used to
initiate the process.Comment: 8 pages with 7 eps figures; uses revtex4. Added references, cleaner
figure
Coherently controlled entanglement generation in a binary Bose-Einstein condensate
Considering a two-component Bose-Einstein condensate in a double-well
potential, a method to generate a Bell state consisting of two spatially
separated condensates is suggested. For repulsive interactions, the required
tunnelling control is achieved numerically by varying the amplitude of a
sinusoidal potential difference between the wells. Both numerical and
analytical calculations reveal the emergence of a highly entangled mesoscopic
state.Comment: 6 pages, 6 figures, epl2.cl
Scaling property of the critical hopping parameters for the Bose-Hubbard model
Recently precise results for the boundary between the Mott insulator phase
and the superfluid phase of the homogeneous Bose-Hubbard model have become
available for arbitrary integer filling factor g and any lattice dimension d >
1. We use these data for demonstrating that the critical hopping parameters
obey a scaling relationship which allows one to map results for different g
onto each other. Unexpectedly, the mean-field result captures the dependence of
the exact critical parameters on the filling factor almost fully. We also
present an approximation formula which describes the critical parameters for d
> 1 and any g with high accuracy.Comment: 5 pages, 5 figures. to appear in EPJ
Collective Oscillations of an Imbalanced Fermi Gas: Axial Compression Modes and Polaron Effective Mass
We investigate the low-lying compression modes of a unitary Fermi gas with
imbalanced spin populations. For low polarization, the strong coupling between
the two spin components leads to a hydrodynamic behavior of the cloud. For
large population imbalance we observe a decoupling of the oscillations of the
two spin components, giving access to the effective mass of the Fermi polaron,
a quasi-particle composed of an impurity dressed by particle-hole pair
excitations in a surrounding Fermi sea. We find , in agreement
with the most recent theoretical predictions.Comment: 4 pages, 4 figures, submitted to PR
Fractional photon-assisted tunneling in an optical superlattice: large contribution to particle transfer
Fractional photon-assisted tunneling is investigated both analytically and
numerically for few interacting ultra-cold atoms in the double-wells of an
optical superlattice. This can be realized experimentally by adding periodic
shaking to an existing experimental setup [Phys. Rev. Lett. 101, 090404
(2008)]. Photon-assisted tunneling is visible in the particle transfer between
the wells of the individual double wells. In order to understand the physics of
the photon-assisted tunneling, an effective model based on the rotating wave
approximation is introduced. The validity of this effective approach is tested
for wide parameter ranges which are accessible to experiments in double-well
lattices. The effective model goes well beyond previous perturbation theory
approaches and is useful to investigate in particular the fractional
photon-assisted tunneling resonances. Analytic results on the level of the
experimentally realizable two-particle quantum dynamics show very good
agreement with the numerical solution of the time-dependent Schr\"odinger
equation. Far from being a small effect, both the one-half-photon and the
one-third-photon resonance are shown to have large effects on the particle
transfer.Comment: 9 pages, 11 png-figure
Strong coupling expansion for the Bose-Hubbard and the Jaynes-Cummings lattice model
A strong coupling expansion, based on the Kato-Bloch perturbation theory,
which has recently been proposed by Eckardt et al. [Phys. Rev. B 79, 195131]
and Teichmann et al. [Phys. Rev. B 79, 224515] is implemented in order to study
various aspects of the Bose-Hubbard and the Jaynes-Cummings lattice model. The
approach, which allows to generate numerically all diagrams up to a desired
order in the interaction strength is generalized for disordered systems and for
the Jaynes-Cummings lattice model. Results for the Bose-Hubbard and the
Jaynes-Cummings lattice model will be presented and compared with results from
VCA and DMRG. Our focus will be on the Mott insulator to superfluid transition.Comment: 29 pages, 21 figure
Synthesis of Peptides from α- and β-Tubulin Containing Glutamic Acid Side-Chain Linked Oligo-Glu with Defined Length
Side-chain oligo- and polyglutamylation represents an important posttranslational modification in tubulin physiology. The particular number of glutamate units is related to specific regulatory functions. In this work, we present a method for the synthesis of building blocks for the Fmoc synthesis of peptides containing main chain glutamic acid residues that carry side-chain branching with oligo-glutamic acid. The two model peptide sequences CYEEVGVDSVEGEG-E(Ex)-EEGEEY and CQDATADEQG-E(Ex)-FEEEEGEDEA from the C-termini of mammalian α1- and β1-tubulin, respectively, containing oligo-glutamic acid side-chain branching with lengths of 1 to 5 amino acids were assembled in good yield and purity. The products may lead to the generation of specific antibodies which should be important tools for a more detailed investigation of polyglutamylation processes
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